Method for bending tubing

ABSTRACT

THE SUBJECT INVENTION RELATES TO A UNIQUE METHOD FOR BENDING RIGID METALLIC TUBING OR OTHER LIKE TUBULAR PRODUCTS. THE PROCESS ASSURES AN EFFECTIVE INTERNAL SUPPORT FOR THE WALLS OF THE TUBING DURING BENDING AND GENERALLY COMPRISES THE STEPS OF ANNEALING, INSERTING A COMPRESSIBLE MANDREL, COLD BLENDING THE TUBING AND REMOVING THE MANDREL SO THAT THE TUBING IS READY FOR FURTHER FABRICATION AND ASSEMBLY STEPS.

United States Patent 3,561,247 METHOD FOR BENDING TUBING Louis A. Pfafman, 318 Yale Ave., Stratford, NJ. 08084; and Michael P. McNally, 128 E. Military Road, and Charles A. Freeberg, 315 Asbury Ave., both of National Park, NJ. 08063 No Drawing. Filed Aug. 27, 1968, Ser. No. 755,725 Int. Cl. B21d 9/01 U.S. Cl. 72-369 1 Claim ABSTRACT OF THE DISCLOSURE The subject invention relates to a unique method for bending rigid metallic tubing or other like tubular products. The process assures an effective internal support for the walls of the tubing during bending and generally cornprises the steps of annealing, inserting a compressible mandrel, cold bending the tubing and removing the mandrel so that the tubing is ready for further fabrication and assembly steps.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates particularly to a method for cold bending radar waveguide tubing utilizing reuseabl mandrels instead of molten rosin filling.

Presently, the process generally used for bending waveguides, pipes, ventilation ducting or like tubing comprises the steps of annealing and cleaning the entire length of tubing, heating a rosin material and filling the tubing with said rosin, cooling the rosin filled tubing, bending the tubing to the required shape, heating the tubing to melt out the rosin therefrom and cleaning and preparing the tubing for further work. However, the heating and handling of molten rosin in the foregoing process presents a number of serious problems. Among the most serious disadvantages encountered in the use of molten rosin is the inherent fire hazard and the danger of painful burns and injuries to operating personnel. Also, damage may occur to the tubing during removal of the rosin and the accompanying fumes and smoke create a considerable ventilation and nuisance problem. In addition, because of the diificulty and extreme care required in handling and removing the rosin from the tubing, an excessive amount of time is required to produce a simple bend in a single tube, which time is increased proportionately when the number of tubes to be'bent is large.

It is another object of the present invention to provide provide a novel and improved process for bending waveguide tubing or the like that overcomes the above and other disadvantages of prior art methods of this type.

It is a further object of the present invention to provide novel and improved method for the bending of metallic tubing which will eliminate the use of molten rosin, thereby increasing the safety factor and reducing the time necessary for such an operation.

It is another object of the persent invention to provide a novel and improved bending method for tubing or the like which minimizes deformation during bending by providing support for the walls of said tubing.

A still further object of the present invention is to provide a novel and improved tubular bending method and associated apparatus which is relatively simple in construction and operation and yet highly reliable in use.

These and other objects of the invention are accomplished by inserting a readily compressible, nonhardening mandrel in the tubing which supports the walls of said tubing during bending whereby a distortion-free bend is produced.

3,561,247 Patented Feb. 9, 1971 Initially, the waveguide or like tubing to be bent is cut to the required size and the edges of the tubing are filed smooth at their ends. The tubing is then annealed in the section where the bend is to be made so as to reduce some of the hardness and brittleness inherent in the metal. After the tubing has been allowed to cool down, it is thoroughly cleaned, for example, by using an acid bath, and inspected to assure that all foreign matter and metallic chips have been removed.

A mandrel or support-plug made from a solid block of polytetrafluoroethylene or fluorinated ethylene propylene, such as Teflon (E. I. du Pont de Nemours and Co.), is machined to the internal dimensions of the tubing with a clearance of .005 to .008 of an inch. This amount of clearance is critical in producing distortion-free bends by providing support for the walls of the tubing during bending. It is to be noted that any other suitable conventional material may be used in place of Tefion if said material has similar characteristics of nonhardening, is readily compressible with the ability to resume its normal shaped after deformation and has a low coeificient of friction. The leading edges of the mandrel are rounded slightly to aid in insertion into the tubing, as will become more apparent hereinafter.

After the proper mandrel is prepared for use, it is inserted in the tubing and positioned by pushing and applying pressure thereon until the center of the mandrel is in the center of the bend area. The length of each mandrel is governed by the longest bend normally made on the applicable size tubing. A length of at least 6 inches is added to this dimension to facilitate ease of handling and for attaching a device to aid in withdrawing the mandrel after the section of tubing is bent.

Once the mandrel is properly positioned in the tubing, the bend is made using the same conventional devices normally used in other cold bending methods, such as, a pneumatic ram bender. The mandrel is then extracted from the bent tubing while the tubing is still in the bending machine or after it has been removed therefrom and placed in a machinists vise. The mandrel is removed from the tubing by using a small hand winch, hydraulic jack or puller hooked to a rod which is provided in one end of the mandrel. Two methods of attaching the pulling device are preferably used. In the first, used on small size tubing, a hole is drilled in the center of the tubing, approximately 1 inch from the end, large enough to receive a nut of the size suitable for a pulling rod. A second hole is drilled from the center of the end of the mandrel into the first hole to receive the pulling rod. A threaded pulling rod is inserted from the end of the mandrel and screwed into the nut placed in the first hole. The second method, used on larger size tubing, is to undercut the mandrel about 3 inches along its length and rivet to it a fabricated metal clip to which the pulling rod is attached. Once the mandrel is extracted, the tubing is ready for further fabrication and assembly steps.

Tubing bent in accordance with the above described method has been found to produce better distortion free bends, particularly with tubing of a smaller radius. In actual production, it was found that the start-to-finish time, as compared to the generally used rosin method, is reduced by more than one-half. In addition, by employing the inventive method, spoilage of the material (rosin) used to support the Walls of the tubing during bending is reduced and the life expectancy of the support mandrels is estimated to be upwards of 500 bends before wear will effect its use.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within 4 the scope of the appended claim, the invention may be (e) cold bending said section of the tubing; practiced otherwise than as specifically described. (f) and extracting the mandrel from the bent tub- What is claimed is: ing. 1. A method of bending a length of rigid metallic tubing comprising the steps of: 5 References Cited (a) annealing the tubing in the section to be bent; UNITED STATES PATENTS (b) cleaning the tubing to remove foreign matter and metallic chips; 423,544 3/ 1890 Vanderman 72-466 (c) machining a Teflon mandrel to the internal dimen- 425,395 4/1890 Wmgate at a] 72-466 zifogls1 icjcltlhe tubing with a clearance of .005 to .008 10 LOWELL A SO P i y Examiner (d) inserting and positioning the mandrel within the U S C1 XR tubing to support the walls of the tubing in the section to be bent; 72-466 

